Process for extracting alumina from feldspar.



UNITED s'ra'rs PATENT FFIGE.

SAMUEL PEACoCK, or CHICAGO, ILLINOIS.

PROCESS EOE EXTRACTIN'G ALUMINA FROM FELDSPAlR.

Specification of Letters Patent.

PatentedAug. 27', 1912.

No Drawing. Original application filed April 8-, 1911, Serial No. 619,829. Divided and this applicatihn-ffiled May 15, 1912.

To all whom it may concern:

Be it known that I, SAMUEL PEACOCK, a citizen of the United States, residing at- Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Processes for EX-.

tracting Alumina from Feldspar; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a process for extracting alumina during the extraction of potash from feldspar, and has for its object to recover said alumina in a pure state while recovering the potassium in the form of an oxid K 0, employing caustic lime in order to. fix the silica as an insoluble silicate of lime, all as is disclosed and claimed in my copending application #619,829, entitled Process for extracting alumina and pot.- ash from feldspar, and filed April 8, 1911, of which this application is a division.

With these and other objects in view, the invention consists in the novel steps constitutin my dprocess more fully hereinafier disclose an particularly pointed out in the claim.

As is well known, a typical feldspar con-' tains SiO A1 0,, Fe O K O,-Na OaO and MgO; andthere are a number of processes known or in use'for. therecoveryofthe potash from feldspaigwhich involve-the formation of calcium silicates and. alkaline aluminates. One of the industrial'deiects in most of these processes, however, is, no-

account is taken of the. factthat the. tempeiiature of formation. of calcium silicate by the dry process, a large proportion of, the potash or soda present will bedriven off by volatilization, and therefore the recovery of the alumina as such'will be far below the quantity represented by the computed aluminate, due to its compounds with lime. On the other hand, ifa considerable excess of potash ori soda is added'to counter-act these objections, the silica willfcombine proportionately with alkali and lime, in accordance'wit-h the law ofmas's action, and

- the recovery of the alumina by forming a.

soluble aluminum salt,is defeated,-

Serial No. 697,562;

In carrying .out my process, I first coarsely crush a mixture of feldspar or similar aluminiferous mineral to be decomposed, and add sufficient carbonate of lime to supply at least one and not more than two chemical equivalents of calcium oxid CaO to each chemical equivalent of silica Si() 'in the mixture. I then subject the "mixture to a temperature suflicient to convert all the crystalline mineral material into the amorf ph'ous form. This later operation ispreferably conducted in a rotary kiln such asjs ordinarily used in the manufacture of cement.

I have discovered, as is pointed out :in my said application above, in calcining'minerals containing potash and another metallic onid which may develop basicproperties such as lime, to a point suflicient to destroy the crystalline structure of the mineral, that all or 'substantially ail of the potash present is displaced or removed by volatilization, By adding lime-stone, however, before the cal-' cination takes place there is produced a potash carrying gas comparatively high in carbon-dioxid CO which may. be utilized at a later sta e in the process, as will appear below, and y scrubbing such gas as it exits from the kiln any volatilized potash may be recovered as a carbonate. After the mineral material is calcined, itis pulverized to not less than say 100 mesh as is usually done in the manufacture of Portland cement, and it is then carefully sampled and. its constituents determined. To the pulverized mineral I next-add sufiicient potash or soda recovered as above,'or otherwise obtained, "to make, "when computed with the potash or code. that has been found to-already exist in the calcined. and pulverized material, one chemical equivalent of potash or soda to each chemical equivalentof alumina present.

The mixture is next boiled, preferably 1111-- der pressure, and withsuficient water to comes soluble as an alkaline aluminate and eke a; thin paste,- The alumina then'be-- I char e are next separated as byifiltrationy and t e soluble.alkalinealuminate isi'ti'eatedf ,with carbon dioxid by means of; which nearly all the alkali is' -s eparated.zfrom fth alumina, producing" insoluble alumina and an alkaline carbonate 1n substantial accord ance with the following react10n:

As is Well known, all of the alkali cannot be separated from the aluminate by this method, as a small proportion forms a compound with that portion of the alumina which resists separation by filtration. This loss of alkali is not of commercial importance, yet its presence in the alumina unfits the latter for certain specific valuable uses,

and therefore reduces the industrial. value of the alumina thus contaminated. In order, therefore, to remove this remaining alkali, the crude alumina resulting from the car bonating process is carefully sampled and its contents of alkali and silica determined. 1 then add to the cruile alumina suflicient amorphous silica to form with such silica as is found present in the crude alumina, one equivalent of silica to each equivalent of soda or potash found present in j he said crude alumina. This mixture is next treated in a digester or autoclave \vith superheated steam under pressure of substantially five atmospheres, more or less, as may be found necessary to decompose all the insoluble alkaline.aluminates. The pressure and time of digestion is found. dependent upon the amount' of insoluble alkaline aluminates presentl lhe digester or autoclave charge 1s=then fitteredwhile hot and thorougl'ily washed'wlth water, Wltll the result that the silica and alkali are removed as an alkali silicate leaving a residuum of alumina practically pure, and suitable for de-hydra-tion at high temperatures, which is adaptable for all the ordinary industrial uses;

The carbon dioxid employed in the treatment of the alkaline aluminate above, may be derived from that driven off fromthe kiln after it has gone through a scrubber, or of course it may be obtained from any other source. The volatilized alkali which escapes from the kiln with said gas is readily recovered in a scrubbing process as a carbonate, and together with the carbonate derived from the alkali alnminate e bow, may be subjected to any suitable and Well known. process of the production oi? the oxid such as K 0, or it may be sold as a carbonate.

What I claim is:

The steps in the process of recovering alumina and potash from feldspar, which consists in suitably producing an alkaline aluminate containing potash from said feldspar; treating the said aluminate with carbon dioxid to separate out a portion of the potash; and then digesting said aluminate with amorphous silica to remove the remainder of said potash, substantially as described.

1n testiniony whereofil. ailix my signature, in presence of tWO Witnesses.

SAMUEL PEACOCK.

R. M. PARKER, T. lVrrnnnsrooN. 

